Social Media WordPress Plugins
Google Author Link
Adds the appropriate metadata to your WordPress posts and pages so that authors can connect Google+ profiles to posts for better SEO. Supports multiple authors.
Instagrate
Easily pull a stream of photos from your instagram account that you can display on your WordPress site in the form of galleries or individual posts with support hashtags and comments.
Social Sharing by Danny
Add share links for sharing on Twitter, Google+ and Facebook to the bottom of your posts and pages in WordPress. Very lightweight, and you can optionally load in icons with CSS and pop-up windows with JS.
Social
Adds the ability to publish post content on both Facebook and Twitter with custom messages, and to pull in social mentions across these sites back into your comments form with a new template.
WP To Twitter
Sync your WordPress site with the Twitter API and customize which posts should be automatically tweeted to your account. Control the content of your tweets, and change settings on a post to post basis with a built-in meta box in your post editor.